Automatic dishwashing detergents (ADD's) used for washing tableware in the home or institutionally in machines especially designed for the purpose have long been known. The particular requirements of cleansing tableware and leaving it in a sanitary, essentially spotless, residue-free state has indeed resulted in so many particular ADD compositions that the body of art pertaining thereto is now recognized as quite distinct from other cleansing product arts. British Patents 1,325,645; 1,527,706; and 1,381,187; European Patent Application EP-A 82,564; and U.S. Pat. Nos. 4,427,417; 4,436,642; and 4,539,144 describe various aspects of ADD's, their components and their manufacture.
In recent times, there has been a renewed interest among consumers in effective, economical cleansing products, especially laundry detergents, using smaller amounts of chemicals and packaging for a diminished environmental impact. In light of legislation and current environmental trends, such products are desirably substantially free of inorganic phosphate builder salts. In addition, such compositions are desirably free of chlorine bleach and "inert" filler ingredients such as sodium sulfate.
Unfortunately, low-dosage nonphosphated ADD products may be made available to the consumer with a promise of effectiveness but in technical terms sacrificing efficacy, especially owing to the loss of phosphate and chlorine mainstay ingredients. Indeed, there does not currently appear to be a commercial low-dosage, nonphosphated ADD product which is economical and at the same time free from end-result shortcomings, such as relatively poor stain removal as compared with the same technology incorporated in regular-dosage nonphosphated formulas. Without being limited by theory, we believe stain removal shortcomings in particular are due to commercial perborate- and perborate-plus-activator ADD products relying quite heavily on a robust product matrix, which is lost in low-dosage product forms unless very expensive high levels of nonphosphorus builder are utilized.
In the course of exploratory studies to address this problem and secure improved low-dosage nonphosphated compositions which are both economical and effective, it has been discovered that perborate, perborate.degree. with-activator (such as tetraacetylethylenediamine) and others among the conventional oxygen bleach technologies are relatively intolerant of significant reductions in levels of alkaline ingredients, builders and "inert" fillers (which actually function as electrolytes), all seemingly vital to successfully arriving at low-dosage forms of the ADD products. Moreover, these shortcomings are especially apparent when the compact-form ADD is used under "stressed" conditions, such as is frequently the case in high-hardness areas or among economy-minded consumers who use products sparingly.
One way round the problem would be to use chlorine bleaches, meaning chlorine-containing compounds which release hypochlorite when dissolved in water; but chlorine bleach limits the formulator since it is incompatible with many desirable components of nonphosphated ADD's, such as enzymes and many nonphosphorus builders and surfactants.
Accordingly, it is an object of the present invention to provide new and improved low-dosage ADD compositions. Such compositions are nonphosphated compositions, i.e., they are substantially free from, and unreliant on inorganic phosphate builders. The compositions herein are also free of chlorine bleach. More specifically, it is an object herein to provide low-dosage solid-form ADD's, especially granules, formulated with monopersulfate ("MPS") salts for highly effective removal of stains from tableware, especially beverage stains such as tea, tea with milk, or coffee, from cups and mugs. Dosages, that is to say usage levels of ADD in automatic dishwashing appliances, are generally from about 25%-70%, more typically from about 50%-60% of the dosage of a conventional phosphated, chlorine-bleach containing automatic dishwashing detergent. Another object herein is to provide a method for washing tableware in home or institutional automatic dishwashing appliances, especially in home appliances, using compositions provided herein at the specific dosage levels further detailed hereinafter.
The unique MPS-containing compositions herein provide numerous advantages in addition to compactness and stain-removal efficacy with economy. These include material protection via a reduced tendency to etch glass and tableware, excellent spotlessness and lack of filming, high water solubility and elimination of undissolved product residue, and the ability to remove proteinaceous food residues from articles such as pots and pans.